1. Field of the Invention
The present invention relates to a process for continuous production of octa-2,7-dien-1-ol comprising reacting butadiene with water.
2. Description of the Related Art
For the production of octa-2,7-dien-1-ol by reacting butadiene with water in the presence of a palladium catalyst, there are several alternative processes. In one of these known processes, butadiene and water are reacted in a co-solvent for both reactants, such as tetrahydrofuran, isopropyl alcohol or tertbutanol in the presence of a catalyst comprising tetrakis(triphenylphosphine) palladium (U.S. Pat. No. 3,670,032). In another process, butadiene and water are reacted in a solvent which is at least partially miscible with both reactants in the presence of a palladium compound complexed with a phosphine ligand such as triphenylphosphine and carbon dioxide to give octa-2,7-dien-1-ol (U.S. Pat. No. 3,992,456). In these processes, the product octa-2,7-dien-1-ol can be separated from the reaction mixture by subjecting the palladium-containing reaction mixture to distillation. However, a detailed study by the present inventors revealed that when the distillation temperature exceeds about 120.degree. C., the palladium catalyst tends to be decomposed to the metal and inactivated. As a production process in which the product octa-2,7-dien-1-ol can be separated from the reaction mixture without resort to distillation, there is a process in which butadiene and water are reacted in the system containing palladium acetate and trisodium salt of tris(m-sulfophenyl)phosphine and the organic phase containing the reaction product is separated from the aqueous phase containing the catalyst by decantation (U.S. Pat. No. 4,142,060). However, because of the extremely poor solubility of butadiene in water, this process has the disadvantage of very low reaction rate and low selectivity to octa-2,7-dien-1-ol.
Since any palladium catalyst of the type which is used in reactions for synthesis of octa-2,7-dien-1-ol are quite expensive catalysts as is well known, the following technical objectives must be achieved in order to produce octa-2,7-dien-1-ol at low cost on a large commercial scale.
1) To achieve a high reaction rate at a commercially permissible palladium catalyst concentration [about several milligram atoms as palladium atom per liter of reaction mixture];
2) To assure a sufficiently high selectivity to octa-2,7-dien-1-ol;
3) To assure that the catalytic activity of the palladium catalyst is maintained over a long time; and
4) To assure that the product octa-2,7-dien-1-ol can be efficiently separated without entailing a deactivation of the palladium catalyst.
To achieve the above technical objectives, two researchers including one of the present inventors have already proposed the following process for producing octa-2,7-dien-1-ol: a process for preparing octa-2,7-dien-1-ol comprising the steps of:
(i) reacting butadiene with water in an aqueous sulfolane solution having a water/sulfolane weight ratio in the range of 20/80 to 70/30 and containing carbonate ions, bicarbonate ions or mixtures thereof, in the presence of (A) palladium or a palladium compound, (B) a monodentate phosphine in an amount of at least 6 moles per gram atom of said palladium; and (C) a monodentate tertiary amine having a basicity constant (pKa) of at least 7 in an amount of 1 to 50% by volume based on the sulfolane to form octa-2,7-dien-1-ol;
(ii) extracting at least part of the reaction mixture obtained in step (i) with a saturated aliphatic hydrocarbon, a monoolefinic hydrocarbon or an alicyclic hydrocarbon; and
(iii) recycling at least part of the extraction residue obtained in step (ii) which contains the catalyst components to step (i) (U.S. Pat. No. 4,356,333 and U.S. Pat. No. 4,417,079).
According to the above process described in U.S. Pat. No. 4,356,333 and U.S. Pat. No. 4,417,079, octa-2,7-dien-1-ol can be produced with high reaction rate and selectivity in a low palladium catalyst concentration and, in addition, can be separated from the reaction mixture without entailing a deactivation of the palladium catalyst, thus permitting re-use of the catalyst by recycling. However, even this improved production process has been found to have several drawbacks which must be surmounted in long-term continuous operation. Thus, it is commercially more efficient, from the standpoint of the ease of recovery of unreacted butadiene and isolation of the product, to increase the conversion of butadiene and the concentration of the product in the reaction mixture as much as possible but actually when the reaction is carried out continuously, there take place a progressive accumulation of insoluble polymer in the reaction system, decreases in selectivity to octa-2,7-dien-1-ol and in reaction rate, and inactivation of the palladium catalyst, all of which were almost negligible in the batch reaction or in a semicontinuous operation up to tens of repeated runs, and these phenomena have been found to seriously interfere with the continuous production of octa-2,7-dien-1-ol. It has also been found that when an extractive procedure is adopted for the separation of octa-2,7-dien-1-ol from the reaction mixture in the process of continuous production of octa-2,7-dien-1-ol under conditions conducive to increased butadiene conversion, the amount of dissolution of the palladium catalyst into the extractant solvent increases with time.